Sheldon Brown has it all on this page:
http://www.sheldonbrown.com/tire-sizing.html
He explains that the 27 is bigger than the 700c, so the tires will not exchange on eachother. I've experienced it myself. My Bridgestone had 27's and I put newer 700c on it. Luckily my long reach brakes worked okay and just had to move the pads lower.
As for the tires, my first question always is "what size is your rim'? The same Sheldon Brown page has a chart at the bottom with recommended sizes for specific rims. On my roadbike I have a 15mm width rim and I use a 28mm training tire. I could go up to a 32, but it doesn't fit under the fender. On my touring bike I have a 17mm rim and use a 32mm touring tire. For my weight (220lbs) the 32 mm tire has been very very comfortable and I enjoy the ride a lot more than the 28mm, but it does go a bit slower. The Kenda you've chosen looks like a very comfy tire and I'd recommend it if you are going to be doing some gravel and packed dirt. If you're going to be doing a lot of paved road, you may find it slowing you down some though.